lastControlID = null;

function toggleDisplay(controlID) {
    if (lastControlID != null && lastControlID != controlID) {
        setDisplay(lastControlID, false);
    }
    controlDisplay =  getDisplay(controlID);
    setDisplay(controlID, !controlDisplay);
    lastControlID = controlID;
}

function setDisplay(id, display) {
    var control = document.getElementById(id);
    control.style.display = (display ? 'block' : 'none');
}

function getDisplay(id) {
    var control = document.getElementById(id);
    
    return !(control.style.display == 'none');
}